The centre says laboratory testing confirms the presence of norovirus in some of the cases and the illness is suspected in the rest of those who have become ill.

An exact source of the contamination has not been determined but the centre says human sewage in seawater is the most likely cause.

Nearly 350 cases of norovirus linked to raw or undercooked B.C. oysters were reported in B.C., Alberta and Ontario starting in late 2016 and continuing through early 2017, forcing the closure of 13 oyster farms on the B.C. coast.

That outbreak was declared over in April 2017, and an article published the British Columbia Medical Journal last June determined sewage spread by ocean currents caused the widespread contamination.

Researchers concluded the outbreak disproved claims that shellfish is safe to eat between September and April, and noted that bacteria, viruses and biotoxins persist in cold sea water year-round.

The centre says it does not recommend eating raw oysters and advises the shellfish should be cooked to an internal temperature of 90 C for 90 seconds to kill pathogens.